Sponge iron, metallized pellets, briquettes, or reduced metal materials such as direct reduced iron ("DRI"), nickel, or the like, are produced by the direct reduction of ores or metal oxides. Large quantities of metallized iron pellets are made in the direct reduction process wherein particulate iron oxide is reduced substantially to metallic iron by direct contact with a reducing gas such as a mixture of hydrogen and carbon monoxide. Throughout this specification and appended claims, the term "metallized pellets" is intended to include metal-bearing pellets such as sponge iron, briquettes, DRI, other compacted forms of reduced metal and the like which contain at least 80 percent of their metal in the metallic state with the balance being primarily in the form of metallic oxide. For these purposes, iron carbide is considered iron in the metallic state. "Metallized" in this specification does not mean coated with metal, but means nearly completely reduced to the metallic state. For ease of discussion and visualization, the majority of this specification will describe the invention as it relates to DRI, although it should be understood that the invention functions equally well with other forms of "metallized pellets" of any size, or any metal.
A problem associated with the use of DRI as a raw material to make steel or other products is its inherent tendency to reoxidize upon exposure to air or water. Exposure of a mass of hot DRI to atmospheric air and moisture causes re-oxidation of the metal ("rusting") with a significant loss of metallization. The re-oxidation also produces heat that can dramatically raise the temperature of a mass of DRI. The process of reoxidation also releases water-bound hydrogen into the immediate environment. Under proper conditions, hot DRI can ignite the liberated hydrogen resulting in additional heat, formation of additional hydrogen and possibly an explosion within transfer piping or within storage units.
DRI must be removed from a direct reduction furnace in order to be useful. Methods are needed to transport DRI while reducing the risk of re-oxidation. One common method of reducing this risk of re-oxidation is to cool the hot DRI material to a sufficiently low temperature (less than about 100.degree. C.), to prevent the ignition of any hydrogen that is released by the oxidation process. One drawback to this method is that current DRI production systems are typically "all or nothing" propositions with respect to cooling. Either all of the hot DRI material exiting a particular furnace is cooled or none of it is cooled.
A known method of transfer is the pneumatic transfer of hot DRI materials through piping from a furnace to an exterior storage unit. Drawbacks to this method include: extensive piping is required to transfer hot DRI through significant elevation changes, input of additional energy is required to the gases utilized in pneumatic transfer, additional opportunities are present for oxygen intake into transfer piping, and size reduction of hot DRI from nugget-size to particulate-size occurs during the transfer to remote storage units because of abrasion and impact.
The present invention does not employ pneumatic transfer, and instead provides a method and apparatus for removing continuous output of hot DRI material from a direct reduction furnace and gravitationally transferring the output for subsequent processing or storage. The invention may simultaneously provide hot DRI material for subsequent steps such as melting or briquetting. The invention may also cool DRI material for transport, storage, or other use.
The disclosure of the invention refers to elements or components in the Midrex process. The Midrex process and apparatus for direct reduction are disclosed in the following U.S. Patents: U.S. Pat. No. 3,748,120 entitled "Method of Reducing Iron Oxide to Metallic Iron", U.S. Pat. No. 3,749,386 entitled "Method for Reducing Iron Oxides in a Gaseous Reduction Process", U.S. Pat. No. 3,764,123 entitled "Apparatus for Reducing Iron Oxide to Metallic Iron", U.S. Pat. No. 3,816,101 entitled "Method for Reducing Iron Oxides in a Gaseous Reduction Process", and U.S. Pat. No. 4,046,557 entitled "Method for Producing Metallic Iron Particles", all of which are hereby incorporated herein by reference.